A control system for a power steering system includes an error module that generates an error signal based on a difference of an estimated output vector and an output vector, a scaling module that calculates a feedback correction signal based on the error signal and an observer gain value, an extended state vector estimation module that determines an extended state vector estimate based on the feedback correction signal and a motor torque command, and a gain module that applies a gain to the extended state vector estimate to generate an estimated driver torque signal, the estimated driver torque signal is applied in control of the power steering system.
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10. A method for controlling a power steering system, the method comprising:
receiving at least an output vector;
generating an error signal based on a difference of an estimated output vector and the output vector;
calculating a feedback correction signal based on the error signal and an observer gain value, the feedback correction signal reducing the difference of the estimated output vector and the output vector by driving the error signal to approach zero;
determining an extended state vector estimate based on the feedback correction signal and a motor torque command; and
applying a gain to the extended state vector estimate to generate an estimated driver torque signal, the estimated driver torque signal assists in control of the power steering system, wherein the extended state vector approaches an actual state vector.
1. A control system for a power steering system, the system comprising:
a processor; and
a memory that includes instructions that, when executed by the processor, cause the processor to:
generate an error signal based on a difference of an estimated output vector and an output vector;
calculate a feedback correction signal based on the error signal and an observer gain value, the feedback correction signal reducing the difference of the estimated output vector and the output vector by driving the error signal to approach zero;
determine an extended state vector estimate based on the feedback correction signal and a motor torque command; and
apply a gain to the extended state vector estimate to generate an estimated driver torque signal, the estimated driver torque signal is applied in control of the power steering system, wherein the extended state vector approaches an actual state vector.
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This patent application claims priority to U.S. Provisional Patent Application Ser. No. 62/213,919, filed Sep. 3, 2015 which is incorporated herein by reference in its entirety.
The present invention relates to a control system for an electric power steering system, and more particularly to a control system for estimating a driver torque based on a model based estimation.
An electric power steering (EPS) system may employ a torque sensor located between a steering column and a rack and pinion assembly. The torque sensor can measure the torque applied at the pinion and also serve as an approximation of the input torque applied to the steering wheel by the vehicle operator (e.g. driver). The output of the torque sensor may be used in calculations to determine an amount of assist torque provided by the motor.
Although the torque sensor can approximate the driver torque during steady state operations, the torque sensor measurement typically deviates from the driver torque during dynamic transients or during large rack force disturbances, such as when a driver releases the steering wheel, or when a driver subjects the vehicle to driving on a bumpy road, for example. A driver torque sensor can be added on the steering wheel to allow for an accurate measurement at an increased cost.
Accordingly, it is desirable to accurately estimate a driver torque in electric power steering system.
In one embodiment, a control system for a power steering system comprises an error module that generates an error signal based on a difference of an estimated output vector and an output vector, a scaling module that calculates a feedback correction signal based on the error signal and an observer gain value, an extended state vector estimation module that determines an extended state vector estimate based on the feedback correction signal and a motor torque command, and a gain module that applies a gain to the extended state vector estimate to generate an estimated driver torque signal, the estimated driver torque signal is applied in control of the power steering system.
In another embodiment, a method for controlling a power steering system comprises generating an error signal based on a difference of an estimated output vector and an output vector, calculating a feedback correction signal based on the error signal and an observer gain value, determining an extended state vector estimate based on the feedback correction signal and a motor torque command; and applying a gain to the extended state vector estimate to generate an estimated driver torque signal, the estimated driver torque signal assists in control of the power steering system.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same, an exemplary embodiment of a vehicle 10 including a steering system 12 is illustrated. In various embodiments, the steering system 12 includes a handwheel 14 coupled to a steering shaft 16. In the exemplary embodiment shown, the steering system 12 is an electric power steering (EPS) system that further includes a steering assist unit 18 that couples to the steering shaft 16 of the steering system 12 and to a left tie rod 20 and a right tie rod 22 of the vehicle 10. It should be noted that the steering system 12 may be a rack assist EPS (REPS) as well. The steering assist unit 18 includes, for example, a rack and pinion steering mechanism (not shown) that may be coupled through the steering shaft 16 to a steering actuator motor and gearing. During operation, as the handwheel 14 is turned by a vehicle operator, the motor of the steering assist unit 18 provides the assistance to move the left tie rod 20 and the right tie rod 22 which in turn moves left and right steering knuckles 24, 26, respectively. The left knuckle 24 is coupled to a left roadway wheel 28, and the right knuckle 26 is coupled to a right roadway wheel 30 of the vehicle 10.
As shown in
A control module 50 controls the operation of the steering system 12 based on one or more of the sensor signals and further based on the steering control systems and methods of the present disclosure. In one embodiment, the control module 50 includes a driver torque estimation module 60. The driver torque estimation module 60 receives input signals that are measured signals of the EPS system. The driver torque estimation module 60 may estimate a driver torque based on the input signals received from a plurality of sensors, for example. The input signals can include but are not limited to a motor command, a t-bar torque signal as measured by the torque sensor 31 on the pinion or handwheel 14, a motor position signal and a motor velocity signal.
Inputs to the control module 50 may be generated from the torque sensor 31 (
In
The input signals are typically scaled in the handwheel coordinate, as some of the signals may have been originally provided in a motor coordinate by respective sensors. In some embodiments, the input signals are scaled into the handwheel coordinate by a mechanical ratio N and gear efficiency E. Alternatively or additionally, the input signals provided to the driver torque estimation module 60 can include a reference motor current signal, a measured motor current signal, a measured handwheel position, measured handwheel velocity, and a calculated motor torque, among other signals.
The measured input signals are used by the driver torque estimation module 60 to determine an estimated driver torque signal. The estimated driver torque signal can be used by the power steering system for further compensation of the handwheel and the EPS. In some embodiments, a three-mass mechanical model of the EPS system can be stored in the driver torque estimation module 60. The three-mass mechanical model can be used to represent system dynamics in the determination of the driver torque estimation. A three-mass EPS mechanical model is described in SAE 1999-01-0399, Badawy et al., Modeling and Analysis of an Electric Power Steering System, which is incorporated by reference herein. However, other mass models (e.g. one mass model, two mass model, ten mass model, etc.) may be used by the driver torque estimation module 60 in the estimation of the driver torque. The driver torque observer may use the mechanical model to determine the driver torque estimation based on the input signals. In some embodiments, the three mass model may take into account rack inertia, handwheel inertia, and motor inertia, among other factors. The mechanical model can be represented by a state space model based on the following state space equations:
{dot over (x)}(t)=Ax(t)+Bu(t) (Equation 1)
y(t)=Cx(t) (Equation 2)
In Equation 1, u(t) is an input vector as a function of motor torque, x(t) is an extended state vector as a function of handwheel position, handwheel velocity, motor position, motor velocity, rack position, rack velocity, driver torque. In Equation 2, y(t) is an output vector as a function of handwheel torque, motor position, and motor velocity. A, B, and C are matrices of the state space equations.
The driver torque estimation module 60 estimates non-measured states of the EPS system. In some embodiments, the driver torque estimation module 60 can use an extended state vector that includes an estimated driver torque state. The driver torque estimation module 60 is shown in more detail in
In operation, a motor torque may be applied to an EPS system 62 by a permanent magnet synchronous motor. The EPS system 62 may be subject to a disturbance, including but not limited to, road jarring or a release of the handwheel by a driver during a steering operation. Accordingly, the actual driver torque acting on the EPS system may be affected by the disturbance.
The actual driver torque acting on the EPS system 62 may be measured by a sensor modules 64, which may include any number of sensors including the sensors shown in
The error module 66 receives the output vector and an estimated output vector as inputs. The error module 66 calculates an error signal that represents a difference between the output vector and the estimated output vector. The estimated output vector may represent selected estimated sensor signals, where the output vector may represent the actual signals provided by the sensor modules 64. The error signal is sent to the scaling module 70, which calculates a feedback correction signal.
In operation, the scaling module 70 scales the error signal to generate the feedback correction signal. In one embodiment, the feedback correction signal represents errors between measured and estimated values of handwheel torque, motor position, and motor velocity signals that have been scaled. To generate the feedback correction signal, the scaling module 70 multiplies the error signal by an observer gain value. The observer gain value may be a matrix designed at least in part using steady-state Kalman filtering or pole-placement method, as described by Gene F. Franklin, J. David Powell, and Abbas Etnami-Naeini, “Feedback control of dynamics systems.” Pretince Hall Inc (2006); Gene F. Franklin, S. David Powell, and Michael L. Workman. Digital control of dynamic systems. Vol. 3. Menlo Park: Addison-Wesley, 1998, both of which are incorporated by reference herein.
The feedback correction signal generated by the scaling module 70 reduces the difference of the estimated output vector and the output vector by driving the error signal to approach zero.
In part, by allowing the feedback correction signal to approximate a zero error signal (e.g. zero value), the driver torque estimation module 60 estimates a driver torque that tracks the actual driver torque. The estimation of the driver torque is determined without an additional sensor specifically to measure the driver torque.
The feedback correction signal is sent to the extended state vector estimation module 68. The extended state vector estimation module 68 generates an extended state vector estimate.
In addition to receiving the output vector from the sensor modules 64, the driver torque estimation module 60 receives the motor torque command. In some embodiments, the motor torque command may be received by the state vector estimation module 68 of the driver torque estimation module 60.
The extended state vector estimation module 68 applies the motor torque command to a set of extended state space equations, which in one embodiment can include the equations described in equations 1 and 2. The extended state vector estimation module 68 further applies a feedback correction signal estimated by the scaling module 70 to the extended state space equation, thereby generating the extended state vector estimate. The extended state vector estimate may be represented by {circumflex over (x)}(t), which in some embodiments, is a function of handwheel position (x_hw), handwheel velocity ({dot over (x)}_hw), motor position ({dot over (x)}_mot), motor velocity ({dot over (x)} mot), rack position (x_am), rack velocity ({dot over (x)}_am), and driver torque (T_dr).
{circumflex over ({dot over (x)})}(t)=A{circumflex over (x)}(t)+Bu(t)+L(y−ŷ) (Equation 3)
The extended state vector estimate is sent to a sensor estimation module 69, which uses the extended state vector estimate to calculate the estimated output vector. In some embodiments, the sensor estimation module 69 selectively filters the extended state vector estimate. Thus, the signals of the estimated output vector may correspond to the signals of the output vector. In some embodiments, the sensor estimation module 69 applies a selection matrix to reduce the extended state vector estimate to the estimated output vector.
The extended state vector estimate acts to reduce a magnitude of the error signal. The extended state vector estimate approaches the actual state vector. In some embodiments, the extended state vector estimate is multiplied by a fixed gain value by a gain module 72, to generate an estimated driver torque.
As noted above, the estimated output vector may represent an estimated t-bar torque, an estimated motor position, and an estimated motor velocity. However, it is further contemplated and understood that the error module may receive an estimated output vector and an output vector that include other EPS signals.
Referring to
In particular, inputs to the controller 410 of the control module 50 (
The hand wheel return module 408 receives as input vehicle speed 420 and hand wheel angle 422. The hand wheel angle 422 may be, for example, an angular position of the hand wheel relative to the center position of the hand wheel 404. The hand wheel return module 408 determines a return command 424 based on the vehicle speed 420 and the hand wheel angle 422. In various embodiments, the hand wheel return module 208 determines the return command 424 using one or more hand wheel return lookup tables 425. The lookup tables 425 can be indexed by the vehicle speed 420 and/or the hand wheel angle 422. The lookup tables 425 can be stored in and accessed from the table datastore 414.
In one example, the hand wheel return module 408 is associated with nine return tables 425. A vehicle speed 420 is defined for each of the nine return tables. A return curve is defined by the data points in the nine return tables. For example, each of the nine return curves is composed of sixteen data points. The data points are defined by the axis, where the axis is defined by hand wheel angle 422. In one example, the hand wheel angle 422 can range from zero to nine-hundred degrees. In various embodiments, the axis can be selectable. In various embodiments, all return curves share a common axis. As can be appreciated, the data of the return curves can be increasing or decreasing. The speed defined for curve zero can be used as a return speed breakpoint (e.g., return command is ramped to zero below the breakpoint speed).
As shown in
The blending strategy described in
Referring now to
Referring to
The hands off wheel calculation module 700 receives an estimated driver torque signal 780 from the driver estimation module 60 (
The envelope detector 772 determines an envelope of the filtered estimated driver torque signal 784, and produces a HOW detection signal 788 as output. The HOW detection signal 788 represents the envelope E of the filtered estimated driver torque signal 784 at a given point in time. The envelope detector 772 may use any number of envelope detection approaches to determine the HOW detection signal 788. For example, in software-based approach the envelope detector 772 passes the filtered estimated driver torque signal 784 to a low pass filter (not illustrated), and then determines an absolute value of the filtered estimated driver torque signal 784. The HOW detection signal 788 is then sent to the HOW state detector 774.
The HOW state detector 774 monitors the HOW detection signal 788 and determines if the HOW condition exists based on comparing the value of the HOW detection signal 788 with a threshold torque value over a predetermined time interval. If the HOW condition is determined to exist, then a HOW signal 710 is generated by the HOW state detector 774 and sent to the torque assist generation module 776. In one embodiment, the HOW state detector 776 may determine the level of force a driver may have on the hand wheel. For example, a HOW medium signal 712 indicates a relatively moderate level of force, and a HOW high signal 714 indicates a relatively high level of force. If the state detector 774 does not send either the HOW signal 710, the HOW medium signal 712, or the HOW high signal 714 to the torque assist generation module 776, then the hands off wheel condition exists. In the exemplary embodiment as shown in
In the embodiment as shown in
In one embodiment, the threshold torque values T may be adjusted based on the speed of the vehicle. The speed of the vehicle is monitored by the vehicle speed sensor. The driver estimation module 60 receives as input a vehicle speed signal 7120 from the vehicle speed sensor. The vehicle speed signal 7120 is sent to a lookup table 7122. The lookup table 7122 is used to determine modified torque threshold values T′ based on the vehicle speed signal 7120. The modified torque threshold values T′ are then sent to the HOW state detector 774. Specifically, the modified torque threshold values T′ include an OFF threshold value 790′, an ON threshold value 792′, a Medium Threshold OFF value 794′, a Medium Threshold ON value 796′, a High Threshold OFF value 798′, and a High Threshold ON value 7100′. The modified torque threshold values T′ may be used in place of the torque threshold values T by the state detector 774.
A first timer T1 and a second timer T2 are provided for each of the ON/OFF sub-module 7104, the medium sub-module 7106, and the high sub-module 7108. Specifically, the ON/OFF sub-module 7104 is in communication with a first timer T1 and a second timer T2, the medium sub-module 7106 is in communication with a medium first timer T1 and a medium second timer T2, and the high sub-module 7108 is in communication with a high first timer T1 and a high second timer T2.
The ON/OFF sub-module 7104 of the HOW state detector 774 monitors the HOW detection signal 788 until the ON/OFF sub-module 7104 determines that the HOW detection signal 788 is greater than the ON threshold value 792. Upon determining the HOW detection signal 788 exceeds the ON threshold value 792, the ON/OFF sub-module 7104 sends a start timer signal 7130 to both the first timer T1 and the second timer T2. The first timer T1 is configured to count up from a first interval of time when receiving of the start timer signal 7130, and the second timer T2 is configured to count up from a second interval of time when receiving of the start timer signal 7130. The first interval of time and the second interval of time are calibratable values that maybe adjusted based on the type of application. In one embodiment, the first interval of time of the first timer T1 is less than the second interval of time of the second timer T2. The ON/OFF sub-module 7104 continues to monitor the HOW detection signal 788 as the first timer T1 counts up from the first interval of time. It should be noted that the first timer T1 and the second timer T2, the medium first timer T1, the medium second timer T2, the high first timer T1 and the high second timer T2 each run concurrently with one another.
The first timer T1 sends a Timer 1 expired signal 7134 to the ON/OFF sub-module 7104 once the first interval of time has expired. Once the Timer 1 expired signal 7134 is received by the ON/OFF sub-module 7104, then the ON/OFF sub-module 7104 determines if the HOW detection signal 788 has remained above the ON threshold value 792 during the first interval of time. If the HOW detection signal 788 has remained above the ON threshold value 792 during the first interval of time, then the HOW condition exists. The state detector 774 is set to a HOW=1 state (e.g., a HOW On state exists), and the ON/OFF sub-module 7104 generates the HOW signal 7110. The ON/OFF sub-module 7104 may also send a reset signal 7132 to the first timer T1 and the second timer T2. The reset signal 7132 initializes the first timer T1 back to time=0. The reset signal 7132 causes the second timer T2 to cease counting up, and initializes the second timer T2 back to time=0.
If the HOW detection signal 788 does not remain above the ON threshold value 792 during the first interval of time and the reset signal 7132 is not sent, the second timer T2 may continue to count up until the second interval of time has lapsed, and a Timer 2 expired signal 7136 is then sent to the ON/OFF sub-module 7104. Once the Timer 2 expired signal 7136 is received by the ON/OFF module 7104, then the ON/OFF sub-module 7104 determines if the HOW detection signal 788 has remained below the OFF threshold value 790 during the second interval of time. If the HOW detection signal 788 has remained below the OFF threshold value 790 during the second interval of time, then the HOW condition does not exist. The ON/OFF sub-module 7104 may then send the reset signal 7132 to initialize the first timer T1 and the second timer T2.
A similar approach may be used to generate the HOW medium signal 7112 by the medium sub-module 7106. The medium sub-module 7106 may monitor the HOW detection signal 788. Upon determining the HOW detection signal 788 is greater than the Medium threshold ON value 796, the medium sub-module 7106 sends a start timer signal 7140 to both the medium first timer T1 and the medium second timer T2. The medium sub-module 7106 continues to monitor the HOW detection signal 788 as the first timer T1 counts up from the first interval of time.
The medium first timer T1 sends a Timer 71 expired signal 7144 to the medium sub-module 7106 once the first interval of time has expired. Once the Timer 1 expired signal 7144 is received by the medium sub-module 7106, then the medium sub-module 7106 determines if the HOW detection signal 788 has remained above the Medium threshold ON value 796 during the first interval of time. If the HOW detection signal 788 has remained above the Medium threshold ON value 796 during the first interval of time, then the HOW condition exists. The state detector 774 is set to a HOW Medium state and generates the HOW Medium signal 7112. The medium sub-module 7106 may also send a reset signal 7142 to the medium first timer T1 and the medium second timer T2.
If the HOW detection signal 788 does not remain above the Medium threshold ON value 796 during the first interval of time and the reset signal 7142 is not sent, the medium second timer T2 may continue to count up until the second interval of time has lapsed, and a Timer 72 expired signal 7146 is then sent to the medium sub-module 7106. Once the Timer 2 expired signal 7146 is received by the medium sub-module 7106, then the medium sub-module 7106 determines if the HOW detection signal 788 has remained below the Medium threshold OFF value 796 during the second interval of time. If the HOW detection signal 788 has remained below the Medium threshold OFF value 794 during the second interval of time, then the HOW Medium condition does not exist. The medium sub-module 7106 may then send the reset signal 7142 to initialize the medium first timer T1 and the medium second timer T2.
A similar approach may be used to generate the HOW high signal 7114 by the high sub-module 7108. The high module 7108 monitors the HOW detection signal 788, and upon determining the HOW detection signal 788 is greater than the High threshold ON value 7100, the high sub-module 7108 sends a start timer signal 7150 to both the high first timer T1 and the high second timer T2. The high sub-module 7108 continues to monitor the HOW detection signal 788 as the high first timer T1 counts up from the first interval of time.
The high first timer T1 sends a Timer 1 expired signal 7154 to the high sub-module 7106 once the first interval of time has expired. Once the Timer 71 expired signal 7154 is received by the high sub-module 7108, then the high sub-module 7108 determines if the HOW detection signal 788 has remained above the High threshold ON value 7100 during the first interval of time. If the HOW detection signal 788 has remained above the High threshold ON value 7100 during the first interval of time, then the HOW High condition exists. The state detector 774 is set to a HOW High state and generates the HOW High signal 7114. The high sub-module 7108 may also send a reset signal 7152 to the high first timer T1 and the high second timer T2.
If the HOW detection signal 788 does not remain above the High threshold ON value 7100 during the first interval of time and the reset signal 7152 is not sent, the second timer T2 may continue to count up until the second interval of time has lapsed, and a Timer 72 expired signal 7156 is then sent to the high sub-module 7108. Once the Timer 2 expired signal 7156 is received by the high sub-module 7108, then the high sub-module 7108 determines if the HOW detection signal 788 has remained below the High threshold OFF value 798 during the second interval of time. If the HOW detection signal 788 has remained below the High threshold OFF value 798 during the second interval of time, then the HOW condition does not exist, and the state detector 774 is not set to the HOW High state. The high sub-module 7108 may then send the reset signal 7152 to initialize the high first timer T1 and the high second timer T2.
The torque assist generation module 776 receives as input the HOW signal 7110, the HOW Medium signal 7112, or the HOW high signal 7114 from the HOW state detector 774. The torque assist generation module 776 selectively generates the torque assist command Tassist to create torque nudges in the hand wheel 734 while a lane monitoring system is in assist mode. Specifically, the torque assist generation module 776 may only generate the torque assist command Tassist in assist mode if one of the HOW signal 7110, the HOW Medium signal 7112, or the HOW high signal 7114 is received from the HOW state detector 774. The torque assist generation module 776 may adjust the value of the torque assist command Tassist based on if the HOW signal 7110, the HOW Medium signal 7112, or the HOW high signal 7114 is received. Specifically, the torque assist command Tassist increases as the level of force exerted on the hand wheel 734 increases. For example, if the HOW high signal 7114 is received, then torque assist command Tassist generated may be greater than if the HOW signal 7110 was received. The HOW signal 7110, the HOW Medium signal 7112, or the HOW high signal 7114 from the HOW state detector 774 may also be provided to the lane monitoring system 732, where the lane monitoring system 732 may not switch from the assist mode to the autonomous mode unless the HOW condition exists (e.g., either the HOW signal 7110, the HOW Medium signal 7112, or the HOW high signal 7114 is sent by the state detector 774).
In operation, the torque assist generation module 776 receives a HOW Low command, a HOW Med command, and a HOW High command. The HOW Low command, HOW Med command, and HOW High command are each multiplied by respective gain modules 802, 804 and 806. In one embodiment, gain module 802 multiplies HOW Low command by a value of 0.1, gain module 804 multiplies HOW Med command by a value of 0.3, and gain module 806 multiplies HOW High command by a value of 0.6. The outputs of gain modules 802, 804 and 806 are sent to adder 808, where the outputs are summed, and the sum of the adder 808 is sent to a rate limiter 810 that limits a rate of increase or decrease. The output of the rate limiter 810 is sent to saturation block 812, where a value of 0 to 1 is computed based on the value output from the rate limiter 810. A lane centering command is multiplied with the value output by the saturation block 812 at the product block 814. The product produced by the product block 814 is sent to the saturation limiter 816 to limit a saturation value produced by the product block 814. The output of the saturation limiter is then sent to an adder 818, where the output of the saturation limiter 816 is summed with a vehicle steering motor torque command. The output of the adder 818 is subjected to a second saturation limiter 820, which outputs the Tassist command.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.
Yu, Bo, Varunjikar, Tejas M., Kaufmann, Timothy W., Champagne, Anthony J.
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